【USACO】Prime Palindromes（暴力暴力再暴力）

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把所有符合条件的数全部记下来，扫一遍就行了，这类数最多2W来个

/*ID: 18906421LANG: C++PROG: pprime*/#include<cmath>#include<cstdio>#include<vector>#include<algorithm>using namespace std;const int maxn = 20005;int a,b;int cnt = 0;int prime[maxn];bool is_prime(int v){    int e = sqrt(v) + 1;    for(int i = 2; i <= e; i++)        if(v % i == 0) return false;    return true;}int solve1(){ //1 2    for(int i = 1; i <= 9; i++){        int v1 = i;        int v2 = i * 10 + i;        if(is_prime(v1)) prime[cnt++] = v1;        if(is_prime(v2)) prime[cnt++] = v2;    }}int solve2(){//3 4    for(int i = 1; i <= 9; i++){        for(int j = 0; j <= 9; j++){            int v1 = i * 100  + j * 10  + i;            int v2 = i * 1000 + j * 100 + j * 10 + i;            if(is_prime(v1)) prime[cnt++] = v1;            if(is_prime(v2)) prime[cnt++] = v2;        }    }}int solve3(){//5 6    for(int i = 1; i <= 9; i++){        for(int j = 0; j <= 9; j++){            for(int k = 0; k <= 9; k++){                int v1 = i * 10000  + j * 1000  + k * 100  + j * 10  + i;                int v2 = i * 100000 + j * 10000 + k * 1000 + k * 100 + j * 10 + i;                if(is_prime(v1)) prime[cnt++] = v1;                if(is_prime(v2)) prime[cnt++] = v2;            }        }    }}int solve4(){//7 8    for(int i = 1; i <= 9; i++){        for(int j = 0; j <= 9; j++){            for(int k = 0; k <= 9; k++){                for(int l = 0; l <= 9; l++){                    int v1 = i * 1000000  + j * 100000  + k * 10000  + l * 1000  + k * 100  + j * 10  + i;                    int v2 = i * 10000000 + j * 1000000 + k * 100000 + l * 10000 + l * 1000 + k * 100 + j * 10 + i;                    if(is_prime(v1)) prime[cnt++] = v1;                    if(is_prime(v2)) prime[cnt++] = v2;                }            }        }    }}void init(){    solve1();solve2();solve3();solve4();    sort(prime,prime + cnt);}int main(){    freopen("pprime.in","r",stdin);    freopen("pprime.out","w",stdout);    init();    scanf("%d%d",&a,&b);    for(int i = 0; i < cnt; i++)        if(prime[i] >= a && prime[i] <= b)            printf("%d\n",prime[i]);    return 0;}

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